AHC: Prevent Chinese unification in 221BC

Your challenge, would you choose to accept it, is to prevent Qin to defeat all six states to form the first Chinese empire in our history, with a POD no earlier than 265 BC. That means I would accept ideas that justifiably prevent Qin's victory in the Battle of Changping, or that the assassination attempt on Qin Shi Huang succeeded.

Bonus if China could remain divided, and the written language and measuring units of the seven states could be kept for another 200 years.

Double bonus if a state other than Qin united China at last.

Triple bonus if, instead of a unification, all seven states developed strong individual identities, and at least 3 of them remain divided until present day, though their expansion into other parts of Asia and present day China would not be restricted.

Jing Ke successfully kills the King of Qin in 227 BC.

John Fredrick Parker said:

Jing Ke successfully kills the King of Qin in 227 BC.

Click to expand...

That only delays the Qin's expansion for a while, and does nothing to prevent another Qin ruler from taking over the rest of China. The state was already a hegemonic power in the western areas, and after conquering the Han and Zhao, it gained sufficient resources, territory, and manpower to successfully confront the other four. The Battle of Changping would be a much better PoD, as it could prevent the Qin, not the Zhao, from recovering, as both sides utilized a significant amount of manpower in the conflict.

Of course, Changping was the best POD, but even after that it was far from a done deal for the six states. They still had 30 years, or a generation to prepare before Qin kick start the unification. A Zhao baby born in 260BC (Changping) would be 30 years old by the time Qin launched the final blow (230 BC).

The competency of Qin forces might be declining after years of battles and casualties, notably:
It failed to take Handan after Changping;

In 247 BC, the Alliance of Five States attacked Qin. It was the last alliance against Qin,and Qin lost everything east of Yellow River other than Xingyang.

It was defeated by Li Mu in 232 BC; and

It was defeated again by Chu in 226 BC.

So it was NOT invincible.

Logistics

One way was to prevent the Zhengguo canal from being built.

Since the fall of Zhao and Wei involved prolonged sieges, and the fall of Chu required 600000 troops to be stationed in Chu for 3 years, one must admire Qin's logistic ability to feed such massive armies for prolonged period of time. They did not have

I consider Zhengguo Canal to be the key for this improvement.

Bonus if you can create a rebellion in Sichuan (Shu), which was another breadbasket for Qin, or make Shu an ally of Chu. Jin did this to Chu by creating Wu, who created massive troubles for Chu.

Politics
Make Qin's internal politics more screwed. A king who listen to rumors and execute his general while he is leading an army in a battle was the key for Zhao's failure (think Lian Po and Li Mu), give such a king to Qin (some insecure Lü Buwei's puppet will do) and she would lose much of her advantages.

Diplomacy
Qi and Yan was not allied to Qin, Zhao, Chu, and Wei would not worry about backstabbing while fighting Qin.